This invention relates to an apparatus for cleaning a steam generator by means of a high-pressure lance, which apparatus comprises a base which is to be secured over an opening in the wall of the steam generator to be cleaned and which is provided with a lance passageway wherein the lance is rotatable about the axis thereof and slidable along the axial direction thereof, means for shifting the lance along the axial direction thereof relative to said base and means for rotating the lance about the axis thereof.
Apparatus of this kind are notably used for applying the method as disclosed in Belgian Pat. No. 889,706.
With such methods, the high-pressure lance is brought through an opening in the wall of the generator, into the space adjacent the end of the pipe bundle inside the generator. The high-pressure lance is provided at the end thereof with a spray head which is moved stepwise from the generator center to the wall. In each stepwise movement the spray head can spray between two pipe rows of the pipe bundle. The linear movement of the lance along the lengthwise axial direction thereof can be stopped for a time, and the lance is then rotated, so that the spray head sprays in all directions between the two pipe rows. The loosened sludge is sucked off by means of suction lines, from the generator bottom.
The problem encountered when applying such methods, is in stopping the linear motion of the lance at the proper moment and switching from the linear motion to a rotation of the lance.
In a known apparatus of the above-defined kind, which is used for applying such a method, the problem is solved by mounting the lance on a carriage which is slidable relative to the base, on the outer side of the generator. The lance is shifted together with the carriage, whereby the carriage is guided in guides which are mounted on the base. The revolving motion of the lance is obtained by means of an air motor which is mounted on the carriage, and which drives the lance directly.
Due to the requirement of using a carriage which moves over the same distance as the lance during cleaning, said known apparatus is quite cumbersome and costly.
Moreover the accuracy of shifting the lance is not satisfactory. The center-to-center spacing between the adjacent pipe rows of the steam generator is known and the movement mechanism of the carriage is so adjusted as to have said carriage move each time over such distance. The faults during the displacements add up with each succeeding movement, so that after a large number of rows and thus after a large number of lance movements, the position of the spray head may show a substantial difference relative to the desired position.
Automating the apparatus is also very difficult and this known equipment is also operated by hand on location. This latter feature is an important drawback when the equipment is for example being used for cleaning steam generators in nuclear power stations. In remaining in the vicinity of the generator during cleaning, the operators of the device may be subjected to radio-active exposure.
An object of the invention is to obviate such drawbacks and to provide an apparatus for cleaning a steam generator by means of a high-pressure lance which is of a relatively simple structure, which is very compact, which allows a very accurate working, and which can be automatically remote-controlled.